In a solid-state imaging device such as a CMOS image sensor, along with the reduction in the pixel size, use is sometimes made of a backside illumination structure, which ensures sufficient light is made incident on the photodiode. The backside illumination structure is a structure in which incident light from a subject is applied to a surface opposite to the front surface of a semiconductor substrate on which circuit elements such as transistors are formed, that is, a back surface of the semiconductor substrate. Since a backside illumination type solid-state imaging device is mounted while the back surface of the semiconductor substrate that is a light illumination surface is set up, it becomes necessary to form external terminals on the backside of the semiconductor substrate. Therefore, through electrodes are formed on the semiconductor substrate to penetrate the same and wirings or electrodes formed on the front surface side of the semiconductor substrate are electrically connected to the external terminals on the backside via the through electrodes.
For example, in order to prevent a leak current between an electrode portion including through electrodes and a pixel portion and noise from the electrode portion, a guard ring that electrically isolates the electrode portion and the pixel portion from each other is formed. However, electrical isolation between the electrode portion and the pixel portion becomes insufficient in some cases depending on the formation method of the guard ring. In this case, a leak current may flow via a P-type semiconductor layer on the backside of the semiconductor substrate between the inner portion and outer portion of the guard ring. Therefore, a process for preventing occurrence of a leak current is strongly desired.